title: Cyclooxygenase-2, prostaglandin E2 glycerol ester and nitric oxide are involved in muscarine-induced presynaptic enhancement at the vertebrate neuromuscular junction.
abstract: Previous work has demonstrated that activation of muscarinic acetylcholine receptors at the lizard neuromuscular junction (NMJ) induces a biphasic modulation of evoked neurotransmitter release: an initial depression followed by a delayed enhancement. The depression is mediated by the release of the endocannabinoid 2-arachidonylglycerol (2-AG) from the muscle and its binding to cannabinoid type 1 receptors on the motor nerve terminal. The work presented here suggests that the delayed enhancement of neurotransmitter release is mediated by cyclooxygenase-2 (COX-2) as it converts 2-AG to the glycerol ester of prostaglandin E2 (PGE2-G). Using immunofluorescence, COX-2 was detected in the perisynaptic Schwann cells (PSCs) surrounding the NMJ. Pretreatment with either of the selective COX-2 inhibitors, nimesulide or DuP 697, prevents the delayed increase in endplate potential (EPP) amplitude normally produced by muscarine. In keeping with its putative role as a mediator of the delayed muscarinic effect, PGE2-G enhances evoked neurotransmitter release. Specifically, PGE2-G increases the amplitude of EPPs without altering that of spontaneous miniature EPPs. As shown previously for the muscarinic effect, the enhancement of evoked neurotransmitter release by PGE2-G depends on nitric oxide (NO) as the response is abolished by application of either N(G)-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthesis, or carboxy-PTIO, a chelator of NO. Intriguingly, the enhancement is not prevented by AH6809, a prostaglandin receptor antagonist, but is blocked by capsazepine, a TRPV1 and TRPM8 receptor antagonist. Taken together, these results suggest that the conversion of 2-AG to PGE2-G by COX-2 underlies the muscarine-induced enhancement of neurotransmitter release at the vertebrate NMJ.
authors.affiliation: C. A. Lindgren: Grinnell College, Department of Biology, 1116 8th Ave., Grinnell College, Grinnell, IA 50112, USA. lindgren@grinnell.edu.
authors.forename: Clark A
authors.initials: CA
authors.lastname: Lindgren
authors.forename: Zachary L
authors.initials: ZL
authors.lastname: Newman
authors.forename: Jamie J
authors.initials: JJ
authors.lastname: Morford
authors.forename: Steven B
authors.initials: SB
authors.lastname: Ryan
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Battani
authors.forename: Zheng
authors.initials: Z
authors.lastname: Su
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D001565:Benzoates / Q000494:pharmacology; D002211:Capsaicin / Q000031:analogs & derivatives / Q000494:pharmacology; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000031:analogs & derivatives* / Q000378:metabolism; D063388:Endocannabinoids / Q000378:metabolism; D005989:Glycerides / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D008116:Lizards; D055369:Miniature Postsynaptic Potentials; D009116:Muscarine / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D012583:Schwann Cells / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D044004:Xanthones / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D001565:Benzoates; D052246:Cyclooxygenase 2 Inhibitors; D063388:Endocannabinoids; D005989:Glycerides; D007093:Imidazoles; D013449:Sulfonamides; D013876:Thiophenes; D044004:Xanthones; C518978:prostaglandin E2 glyceryl ester; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009569:Nitric Oxide; C053876:6-isopropoxy-9-oxoxanthene-2-carboxylic acid; D009116:Muscarine; C064874:DuP 697; C094503:glyceryl 2-arachidonate; D051546:Cyclooxygenase 2; D015232:Dinoprostone; C071423:capsazepine; D002211:Capsaicin; C012655:nimesulide; D019331:NG-Nitroarginine Methyl Ester